1. Field of the Invention
The present invention relates to an automatic header height control system. More specifically, the present invention relates to a pulsing automatic header height control method and apparatus which provides for the supply or relief of correction pulses of pressurized hydraulic fluid to or from one end of a piston and cylinder mechanism operable to raise or lower the header, the duration of each pulse being related to the size of the error between the actual header height and the desired header height above ground.
2. Description of the Prior Art
Heretofore various automatic header height control systems have been proposed for controlling the height of a header above ground and for providing an automatic correction when the actual height of the header differs from a selected desired height. Examples of various header height control systems previously proposed are disclosed in the following U.S. patents:
U.S. Pat. No.
3,623,301 PA2 3,704,574 PA2 3,722,193 PA2 3,851,451 PA2 3,886,718 PA2 3,906,710 PA2 3,908,345 PA2 4,136,508
Particular reference is made to U.S. Pat. Nos. 3,704,574, 3,851,451 and 4,136,508.
U.S. Pat. No. 3,704,574 issued to S. H. Gardner on Dec. 5, 1972, for: COMBINE AUTOMATIC HEADER HEIGHT CONTROL discloses a mechanical system associated with header height sensors for moving a valve stem in or out, depending upon the movement of the header height sensor above or below a predetermined setting thereof.
U.S. Pat. No. 3,851,451 issued to J. B. Agness, et al. on Dec. 3, 1974, for: AUTOMATIC HEIGHT CONTROL SYSTEM FOR A CROP HARVESTER discloses an automatic height control system having a plurality of individually operable ground followers or height sensors operatively associated with switches which are electrically connected to a solenoid valve for controlling the vertical movement of a header of a crop-gathering unit.
U.S. Pat. No. 4,136,508 issued to M. W. Coleman, et al. on Jan. 30, 1979, for: CLOSED-LOOP COMBINE HEADER HEIGHT CONTROL discloses an automatic header height control for the crop-gathering header of a combine which permits the operator to change the desired height setting from the operator's platform without stopping the combine and to adjust the dead band within which the header can move from a height setting without generating a correction signal from the operator's platform and do so without stopping the combine. The dead bank adjust includes a potentiometer.
There is also disclosed in U.S. Pat. No. 3,736,486 a dead band control circuit in a servocontrol system for a digital servo-motor control and drive system which is particularly useful in controlling a servo-motor used in editing images in a motion picture film-to-videotape transfer system. The dead band control circuit includes an adjustable potentiometer whereby the dead band can be adjusted quite accurately merely by adjusting the wiper arm of the potentiometer.
As will be described in greater detail hereinafter, the automatic header height control system of the present invention provides a pulsing automatic header height control method and apparatus for effecting, incrementally in pulses, adjustment of the height of a header toward a desired, selected height, the duration of each correction pulse being related to the amount of deviation or error of the actual header height from the selected, desired header height. These pulses are generated electrically and transmlated to control duration pulses of pressurized hydraulic fluid which are delivered to an hydraulic mechanism for raising or lowering the header.
Heretofore, such a pulsing system for automatically controlling header height and providing correction dependent upon the amount of the error has not been proposed. However, there has heretofore been proposed in a non-analogous servo-control system for controlling the position of a butterfly-type valve element in an air duct having an air outlet to a room whose temperature is controlled by inputs from hot and cold air ducts, a regulated control system which provides for pulse duration modulated signals in the dead band zone. This REGULATED CONTROL SYSTEM is disclosed in U.S. Pat. No. 3,083,327, issued to R. C. Byloff on Mar. 26, 1963. In this system, at the edge of the modulated band, full power pulses are generated for moving a valve motor in a clockwise direction or in a counterclockwise direction to move a valve element.
This patent teaches that small error signals which normally would have little effect are utilized to provide control current pulses of full power and varying pulse duration to extend the circuit operation past and into the dead band zone. These control current pulses provide inching operation of the valve motor.
Within the dead band zone, the regulated control system provides full power pulses with varying duration depending upon the amount of error. Outside the dead band zone, the system also provides full power pulses having a duty cycle and/or frequency which are a function of the amplitude of an input, variable amplitude, error signal which is supplied as an input to magnetic amplifier circuits. As the magnitude of error increases, the full power pulses are either of longer duty cycle and/or of higher frequency, until at the edge of the modulation band, full and continuous power is applied to the valve motor. Besides magnetic amplifiers, the system of the Byloff patent includes time constant circuits for controlling the pulse intervals.
Although this patent teaches the concept of changing variable amplitude error signals to pulse duration modulated power pulses, such pulses can be varied in frequency and/or pulse width outside the dead band zone relative to the input error signal received.
In other words, this system starts at the edge of the modulated band with full power output which, as the error reduces, changes to variable duty cycle and/or variable frequency pulses, until the amplitude of the error signal is reduced to a level which places the system in the dead band zone where the variable amplitude input error signal continues to be changed to full power pulses of varying pulse duration, the duration being related to the amplitude of the input signal.
As will be disclosed in greater detail hereinafter, the pulsing automatic header height control method and apparatus of the present invention differ from the REGULATED CONTROL SYSTEM disclosed in the Byloff U.S. Pat. No. 3,083,327 by providing a very small dead band zone with no control within the dead band zone, by providing a system which is utilized for controlling the height of a header as opposed to a butterfly valve element in an air duct, by providing a simple, electronic system without the use of complicated magnetic amplifiers, and by providing for constant amplitude, variable duration pulses from the hysteresis/dead band through a programmed maximum error condition of 30.degree. of potentiometer movement with no full D.C. power application and wherein the duration of each pulse is directly related to the amount of error sensed between the actual header height and the selected, desired header height.